Liquid crystal display devices (LCDs) have been used as display devices in many occasions in recent years. Amongst those, active-matrix-driven LCDs having a thin film transistor for each pixel are widely used in flat-screen television sets, laptop computers, monitors of desktop computers, and the like, because of their low thickness and light weight, and their characteristics such as low-power consumption, high resolution, and high contrast.
The configuration of each active-matrix-driven LCD used today includes a liquid crystal panel (display panel) and a backlight. The liquid crystal panel which includes two glass substrates interposing therebetween liquid crystal has a color filter. On the back surface of this liquid crystal panel, the backlight is provided.
In many cases, the backlight adopted in the active-matrix-driven LCD is a fluorescent lamp (cold-cathode tube) of several mm in diameter, which lamp has a shape of a straight pipe or U-shaped pipe or the like. The fluorescent lamp can be adopted to a “direct method” in which a fluorescent lamp is arranged directly at the back of the liquid crystal panel, or to an area light source adopting an “edge light method” in which a fluorescent lamp is arranged on an edge of an optical waveguide, and light from the fluorescent lamp is delivered to the back surface of the liquid crystal panel via the optical waveguide. Further, in recent years, LEDs are increasingly used as backlight in place of fluorescent lamps.
For example, Patent Document 1 discloses a liquid crystal display device adopting, as a backlight, an FED (Field Emission Display) having emitting pixels corresponding to display pixels of a liquid crystal panel on a one-to-one basis (see FIG. 10).
Meanwhile, it is believed that a liquid crystal display device does not achieve the displaying performance of a CRT in terms of dynamic range of displaying. In view of this, the following technology has been conventionally suggested. Namely, in the art, the luminance of a backlight which is constant in terms of time is varied according to video information, so as to expand the dynamic range of displaying.
Examples of such a technologies are disclosed in Patent Documents 2, 3, or 4. In these disclosed technologies, a backlight is divided into plural emitting regions (illuminating regions) forming a matrix of N×M. For each of the illuminating regions, optimum luminance according to video information is calculated, and the backlight luminance control and image processing based on a video signal are performed for each of the emitting regions. This technology is hereinafter referred to as divided-screen active backlight driving.
As described, the luminance of each emitting region of the backlight is suitably varied based on video information of a corresponding piece of a divided image, thereby displaying the video with a high dynamic range.
However, the technology of Patent Document 1 and the divided-screen active backlight driving disclosed in Patent Documents 2 to 4 have the following problems.
First, when the divided-screen active backlight driving of Patent Documents 2 to 4 is performed in a liquid crystal display device, the arrangement and shape of light sources used in a backlight will restrict the freedom in patterning the backlight into emitting regions.
For example, in cases where fluorescent lamps are used in a backlight as is described in Patent Document 4, straight pipes or U-shaped pipes of several nm in diameter needs to be arranged at a predetermined interval. Accordingly, the number of emitting regions and their shapes are largely dependent on the shapes and arrangement of the fluorescent lamps.
Further, the smallest module of a light source (e.g. fluorescent lamp, LED) defines the smallest emission unit of a division pattern of the emitting regions in the backlight. As such, it is not possible to further divide the light emitting regions into smaller regions than the smallest emission unit.
On the other hand, as described in Patent Document 1, using, as a backlight, an FED having unit emitting pixels corresponding to display pixels of a liquid crystal panel on a one-to-one basis will necessitate that the resolution of the FED be the same as that of the liquid crystal panel (i.e., that the FED have the same number of pixels as the liquid crystal panel). This increases the cost for manufacturing the FED and the cost for a driving system therefor.    Patent Document 1: Japanese Unexamined Patent Publication No. 148829/1998 (Tokukaihei 10-148829; Published on Jun. 2, 1998)    Patent Document 2: Japanese Unexamined Patent Publication No. 99250/2002 (Tokukai 2002-99250; Published on Apr. 5, 2002)    Patent Document 3: Japanese Unexamined Patent Publication No. 350179/2004 (Tokukai 2004-350179; Published on Dec. 9, 2004)    Patent Document 4: Japanese Unexamined Patent Publication No. 321571/2000 (Tokukai 2000-321571; Published on Nov. 24, 2000)    Patent Document 5: Japanese Unexamined Patent Publication No. 228062/2004 (Tokukai 2004-228062; Published on Aug. 12, 2004)    Non-Patent Document 1: Y. Takeuchi, T. Nanataki, I. Ohwada, “Novel Display Panel Utilizing Field Effect—Ferroelectric Electron Emitters”, Proceedings of the 11th International Display Workshops (IDW'04), pp. 1193-1196 (2004), Published on Dec. 8, 2004